Virtual ligand screening of α-glucosidase: Identification of a novel potent noncarbohydrate mimetic inhibitor

5-Thiazoleacetamide derivatives of AR122 and AR125 were screened as α-glucosidase inhibitors by in silico high-throughput screening from commercial drug-like small compound libraries. Inhibition of α-glucosidase with AR122 and AR125 is time dependent: with no preincubation, AR122 and AR125 are relatively moderate inhibitors, but interestingly, after a 120 min incubation, they were 50-fold more potent (AR122: IC(50)=2.47 μM and AR125: IC(50)=27.1 μM). Plots of ln [residual α-glucosidase activity %] versus preincubation time show a pseudo-first order kinetics for both inhibitors. Through dialysis of enzyme-inhibitor complexes, no activity recovery was shown. These results suggest that AR122 and AR125 constitute a new class of noncarbohydrate mimetic inhibitor with an irreversible mechanism.     

Structure-based catalytic optimization of a type III Rubisco from a hyperthermophile

The Calvin-Benson-Bassham cycle is responsible for carbon dioxide fixation in all plants, algae, and cyanobacteria. The enzyme that catalyzes the carbon dioxide-fixing reaction is ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Rubisco from a hyperthermophilic archaeon Thermococcus kodakarensis (Tk-Rubisco) belongs to the type III group, and shows high activity at high temperatures. We have previously found that replacement of the entire α-helix 6 of Tk-Rubisco with the corresponding region of the spinach enzyme (SP6 mutant) results in an improvement of catalytic performance at mesophilic temperatures, both in vivo and in vitro, whereas the former and latter half-replacements of the α-helix 6 (SP4 and SP5 mutants) do not yield such improvement. We report here the crystal structures of the wild-type Tk-Rubisco and the mutants SP4 and SP6, and discuss the relationships between their structures and enzymatic activities. A comparison among these structures shows the movement and the increase of temperature factors of α-helix 6 induced by four essential factors. We thus supposed that an increase in the flexibility of the α-helix 6 and loop 6 regions was important to increase the catalytic activity of Tk-Rubisco at ambient temperatures. Based on this structural information, we constructed a new mutant, SP5-V330T, which was designed to have significantly greater flexibility in the above region, and it proved to exhibit the highest activity among all mutants examined to date. The thermostability of the SP5-V330T mutant was lower than that of wild-type Tk-Rubisco, providing further support on the relationship between flexibility and activity at ambient temperatures.     

Expression of heat shock protein 70a mRNA in Bombyx mori diapause eggs

In an effort to understand whether heat shock protein 70 (Hsp70) participates in the environmental 5 °C signal reception/transduction toward breaking embryonic diapause of the silkworm Bombyx mori, we isolated a cDNA for Hsp70a and examined the expression of Hsp70a mRNA in B. mori diapause and nondiapause eggs by quantitative real-time PCR. Hsp70a mRNA gradually increased in diapause eggs continuously kept at 25 °C after oviposition to maintain diapause. When diapause eggs were exposed to the diapause-terminating condition of 5 °C beginning at 2 days post-oviposition, Hsp70a mRNA increased beginning at 5 days post-cold treatment. Even in nondiapause eggs, Hsp70a mRNA increased slightly with exposure to 5 °C. These results suggest that Hsp70a is involved in reception/transduction of the diapause-terminating (5 °C) signal via gene activation. The expression patterns of Hsp70a mRNA are discussed in relation to those of the cold-response gene Samui.     

Biochemical properties and regulated gene expression of the superoxide dismutase from the facultatively aerobic hyperthermophile Pyrobaculum calidifontis

Superoxide dismutase (SOD) was purified from a facultatively aerobic hyperthermophilic archaeon, Pyrobaculum calidifontis VA1. The purified native protein from aerobically grown cells exhibited 1,960 U of SOD activity/mg and contained 0.86 +/- 0.04 manganese and <0.01 iron atoms per subunit. The gene encoding SOD was cloned and expressed in Escherichia coli. Although the recombinant protein was soluble, little activity was observed due to the lack of metal incorporation. Reconstitution of the enzyme by heat treatment with either Mn or Fe yielded a highly active protein with specific activities of 1,970 and 434 U/mg, respectively. This indicated that the SOD from P. calidifontis was a cambialistic SOD with a preference toward Mn in terms of activity. Interestingly, reconstitution experiments in vitro indicated a higher tendency of the enzyme to incorporate Fe than Mn. When P. calidifontis was grown under anaerobic conditions, a majority of the native SOD was incorporated with Fe, indicating the cambialistic property of this enzyme in vivo. We further examined the expression levels of SOD and a previously characterized Mn catalase from this strain in the presence or absence of oxygen. Northern blot, Western blot, and activity measurement analyses revealed that both genes are expressed at much higher levels under aerobic conditions. We also detected a rapid response in the biosynthesis of these enzymes once the cells were exposed to oxygen.     

Targeted gene disruption by homologous recombination in the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1

In contrast to the high accumulation in sequence data for hyperthermophilic archaea, methodology for genetically manipulating these strains is still at an early stage. This study aimed to develop a gene disruption system for the hyperthermophilic euryarchaeon Thermococcus kodakaraensis KOD1. Uracil-auxotrophic mutants with mutations in the orotidine-5'-monophosphate decarboxylase gene (pyrF) were isolated by positive selection using 5-fluoroorotic acid (5-FOA) and used as hosts for further transformation experiments. We then attempted targeted disruption of the trpE locus in the host strain by homologous recombination, as disruption of trpE was expected to result in tryptophan auxotrophy, an easily detectable phenotype. A disruption vector harboring the pyrF marker within trpE was constructed for double-crossover recombination. The host cells were transformed with the exogenous DNA using the CaCl(2) method, and several transformants could be selected based on genetic complementation. Genotypic and phenotypic analyses of a transformant revealed the unique occurrence of targeted disruption, as well as a phenotypic change of auxotrophy from uracil to tryptophan caused by integration of the wild-type pyrF into the host chromosome at trpE. As with the circular plasmid, gene disruption with linear DNA was also possible when the homologous regions were relatively long. Shortening these regions led to predominant recombination between the pyrF marker in the exogenous DNA and the mutated allele on the host chromosome. In contrast, we could not obtain trpE disruptants by insertional inactivation using a vector designed for single-crossover recombination. The gene targeting system developed in this study provides a long-needed tool in the research on hyperthermophilic archaea and will open the way to a systematic, genetic approach for the elucidation of unknown gene function in these organisms.     

Expression of Binary Toxin Genes in the Mosquito-Colonizable Bacteria, <Emphasis Type="Italic">Bacillus cereus</Emphasis>, Leads to High Toxicity Against <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> Larvae

Two B. cereus strains, Ae10 and Cx5, isolated from mosquito larval guts, were transformed with a recombinant plasmid, pBS373, harboring binary toxin genes from Bacillus sphaericus 2297. Immunoblotting analysis clearly revealed the production and presence of the 51-kDa toxin protein in both strains. Two recombinant B. cereus strains Ae10 and Cx5 showed very high toxicity against C. quinquefasciatus larvae. Since both strains have a close relationship with the mosquito larvae in the native environment and are capable of recolonizing in the guts of mosquito larvae, these strains can be considered promising new hosts for an effective delivery of mosquito-larvicidal toxins.     

Proliferation and differentiation of Xenopus A6 cells under hypergravity as revealed by time-lapse imaging

Xenopus laevis A6 cells, which are cloned epithelial cells from the Xenopus kidney, differentiate into a dome structure when the cells reach confluence. We investigated the gravitational responses of A6 cellular motility during normal differentiation and differentiation under hypergravity conditions using centrifugation (1-100 x g). Progression to dome formation was analyzed by time-lapse micrography. Dome formation and increased expression of Na(+)/K(+)-adenosine triphosphatase were used as markers of differentiation. Interestingly, a high rate of cellular proliferation was observed at a low level of hypergravity (5 x g). Despite this, there was no difference in the time to dome formation between the control cells at primary cell density and those that differentiated under hyper- or hypogravity conditions. In conclusion, this experiment on amphibian cells revealed that the proliferation of A6 cells was strongly affected by gravity conditions, but the differentiation step appears to be controlled by an intra- or intercellular clock.     

Structural and functional diversities of the Aplysia Mytilus inhibitory peptide-related peptides

Aplysia Mytilus inhibitory peptide-related peptides (AMRPs) are multiple hexapeptides coded on a single precursor. By comparing the AMRP precursors of two species of Aplysia (Aplysia californica and Aplysia kurodai), we found that there are substantial numbers of species-specific AMRPs. We next compared the function of AMRPs on the anterior aorta between A. kurodai and Aplysia juliana. In A. juliana, AMRPs inhibited the contractile activity of the aorta (EC(50)=10(-9) to 10(-8)M), whereas the peptides had no obvious action in A. kurodai up to 10(-7)M. These results indicate that AMRPs are both structurally and functionally diverse neuropeptides even among closely related species.